1. Field of the Invention
The present invention relates to a method and apparatus for the control of a write signal, in particular, for use within an optical disc system.
2. Description of the Related Art
Optical disc technology has developed from initial CD formats to more recent DVD formats requiring ever more accurate and readily controllable optical write devices based upon laser technology.
In order to further enhance the control of the laser source, it has been known to develop feedback signals in order to tune the laser power dynamically during recording onto an optical writable, and/or re-writable disk. Such feedback serves to enhance the quality of the recorded signal irrespective of any local variations in optical characteristics of the surface of the disc arising, for example, from fingerprints, dots and/or scratches on the surface of the disc. Through the use of such feedback signals the write quality can be maintained at a relatively consistent level.
In such known systems, the feedback signal is generally derived and calculated on the basis of measurement of the absorption area of the RF signal for discs comprising dye media, or RF signals sampled between writing pulses for discs comprising phase-change media.
The feedback signal can itself be normalised on the reflection signal when seeking to measure the absorption area, or indeed on the laser power signal as derived from the signal returning from the disc and offering an indication of the reflection measurement.
While such known feedback arrangements have proved advantageous in relation to optical discs employing CD writable and re-writable technology, the analogue basis for the measurements required to arrive at the feedback signal do not support DVD writable and re-writable technologies, and in particular the new Write Strategy employed when writing to DVD media.